1. Field of the Invention
The present invention relates to a method for producing a piezoelectric actuator for a liquid transporting apparatus, a method for producing a liquid transporting apparatus, and an apparatus for producing a piezoelectric actuator.
2. Description of Related Art
A liquid transporting apparatus such as an ink-jet head, which discharges ink through its nozzle, has an actuator which exerts pressure on liquid to transport the liquid. Actuators for liquid transporting apparatuses vary in structure, and among others a piezoelectric actuator is widely used which has a piezoelectric layer formed of a ferroelectric piezoelectric material such as lead zirconate titanate (PZT), and in which, when an electric field acts on the piezoelectric layer, the piezoelectric layer deforms to drive an object. For example, a piezoelectric actuator for an ink-jet head generally has a pressure chamber, a vibration plate, a piezoelectric layer and two electrodes. The pressure chambers contain ink and are covered by one side of the vibration plate. The piezoelectric layer is arranged on the other side of the vibration plate. Each of the electrodes is arranged on one side of the piezoelectric layer.
For example, a piezoelectric layer of relatively uniform thickness can be formed by an aerosol deposition (AD) method (see, for example, Japanese Patent Application Laid-open No. 2003-142750) or a sputtering method (see, for example, U.S. Pat. No. 6,347,862 and the corresponding Japanese Patent Application Laid-open No. 10-286953). The aerosol deposition method is a method for blowing very small particles of piezoelectric material mixed with a carrier gas onto a substrate so that the mixture impinges at a high velocity and is deposited on the substrate. The sputtering method is a method for ionizing argon or the like and forcing it to be impinged on a target so that particles of the target are deposited on a substrate. Alternatively, a piezoelectric layer can be formed by joining, to a vibration plate, a piezoelectric sheet obtained by burning (calcining) a green sheet of PZT or the like (see, for example, U.S. Patent Application Publication No. 2004/0223035 and the corresponding Japanese Patent Application Laid-open No. 2004-284109).
In the piezoelectric actuator, when drive voltage is applied to one of the two electrodes, an electric field acts through the piezoelectric layer sandwiched between the electrodes, so that the layer expands in a direction of thickness of the piezoelectric layer and contracts in a direction parallel to a plane of the piezoelectric layer. The deformation of the piezoelectric layer results in the deformation of the vibration plate, therefore a volume of the pressure chamber changes, thereby applying a pressure to the ink in the pressure chamber.
When the vibration plates of actuators are formed of a metallic material, there may be a case in which vibration plates made of metallic sheets are slightly different in thickness per every lot of vibration plate. This results in the vibration plate varying in thickness for each actuator. Consequently, when the thickness of the vibration plates vary, the actuators have various characteristics even if piezoelectric layers of equal thickness can be formed for the actuators by the AD method, the sputtering method or another method, or by using piezoelectric sheets of equal thickness. The actuator characteristics include the deformation of each vibration plate and the rigidity of each piezoelectric actuator. Consequently, the various characteristics among the actuators cause the heads to discharge ink droplets in various volumes at various velocities through their nozzles. This results in the printing quality being uneven, so that the yield lowers.
Conceivably, the variation in thickness among the vibration plates can be corrected by adjusting, for each of the heads, conditions such as, the drive voltage, the drive waveform, for the drive signal supplied to an electrode of each of the heads. However, it is troublesome to correct these conditions for each of the heads, and the correction may be difficult depending on the specifications or the like for the driving units which apply drive voltage to electrodes.